H. Abramovic et C. Klofutar, APPARENT MOLAL VOLUMES OF PECTIC ACID AND SOME TETRA-N-ALKYLAMMONIUM SALTS OF PECTIC ACID, European Polymer Journal, 33(5), 1997, pp. 767-772
From commercially available pectin (OBIPEKTIN AG), pectic acid was iso
lated by alkaline catalysed hydrolysis and physico-chemically characte
rised. The densities of aqueous solutions of tetramethyl-, tetraethyl-
, tetra-n-propyl- and tetra-n-butylammonium pectate were determined at
concentrations up to 0.016 g . cm(-3) with a vibrating tube densimete
r at 298 K. The concentration dependence of the derived apparent molal
volumes and the influence of the nature of the counterion on the appa
rent molal volume was investigated. Thereby, a linear increase in the
apparent molal volume, determined at the reference concentration, with
increasing number of carbon atoms in the counterion was found. The ex
perimental values of the apparent molal volumes approached a logarithm
ic dependence on concentration. The theoretical expression for the con
centration dependence of the apparent molal volumes was interpreted on
the basis of the cell-model of a polyelectrolyte solution and on the
basis of infinite-line-charge theory. The experimental values of the a
pparent molal volumes were found to be higher than theoretical ones in
the concentration range investigated. (C) 1997 Elsevier Science Ltd.
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